This invention relates to the field of track type vehicles, especially track type vehicles having rock drills mounted thereon. More particularly, this invention relates to a track type vehicle in which the tracks are vertically movable, i.e. oscillate, relative to each other to accommodate the terrain.
Track mounted rock drills are often required to traverse uneven and sloped terrain in moving from one position to another, and they are often required to perform their drilling operations on uneven or sloped terrain. To facilitate operation in such terrain, the track mechanism is often endowed with the capability of oscillation, i.e. movement in the vertical plane of one track relative to the other, to permit the tracks to conform to the ground conditions. One well known and particularly effective way to accomplish such oscillation is to construct the track vehicle with pivotable A frame members and a walking beam structure. The walking beam extends between the track assemblies and is pivotally mounted on the main frame of the vehicle. Each leg of the A frame is also connected to one of the track assemblies and is pivotally connected to the main frame of the vehicle. With this arrangement, i.e., pivotal A-frame and walking beam, when a track is forced upward as a result of a change in terrain, the walking beam forces the other track to remain firmly on the ground. This arrangement offers strength in the components of the oscillating system and substantially trouble free service.
Notwithstanding the desirability and advantages of the A-frame and walking beam oscillation construction for track vehicles, one significant disadvantage is encountered with track mounted rock drills having swing booms. If the boom and drill guide assembly is swung to a position where it extends beyond the outer side of one of the tracks, the oscillation system, due to its freedom of movement, and the moment generated by the overhanging boom and drill guide assembly, causes the other track to rise off the ground significantly. In other words, if the boom and drill guide assembly is swung out beyond the forward side of the right track, the rear side of the left track will lift off the ground; and the rear right track will elevate if the boom is swung beyond the side of the left track. This unwanted oscillation in the system prevents the achievement of a firm drilling platform since stinging, i.e. impacting, the ground with the drill guide will result in forcing the raised track to come down, and alignment in the drilling operation is lost. This unwanted oscillation with its resultant loss of alignment in drilling operations is intolerable in many situations.
Several attempts have been made in the prior art to lock out the unwanted track oscillation during drilling operations. One approach has been to incorporate very large adjusting screws which are mounted on the main frame and extend to the walking beam. These screws may be adjusted to prevent pivotal motion of the walking beam. While effective, this approach has the severe disadvantage that actuation of the adjusting screws is time consuming, cumbersome and sometimes difficult to achieve. Accordingly, the operator very often forgets to or elects not to unlock the walking beam, in which event the tracks remain locked out of their oscillation capability, and rough ground maneuverability is lost. This loss of rough ground maneuverability is not only an inconvenience, but it can also be a very serious safety hazard since the vehicle becomes much more susceptible to tipping. The operator may forget that the vehicle has lost maneuverability and may try to direct it over terrain which now becomes dangerous.
Another approach in the prior art is shown in U.S. Pat. No. 2,842,340 to Burress. In this system, the walking beam is eliminated and replaced by a pair of double acting cylinders attached between the main frame of the vehicle and the track assemblies. The system of U.S. Pat. No. 2,842,340 eliminates the walking beam, and track oscillation is accomplished by surging or transferring of fluid from one of the double acting cylinders to the other. Track oscillation may be blocked out by the valve which prevents flow communication between the cylinders. The principal disadvantage of the system of the Burress patent is that the hydraulic system must be relied upon to provide both track oscillation and oscillation lock out. The hydraulic cylinders must be large enough to assume the burden of the whole weight of the system, and both the oscillation system and the lock out system are lost if the hydraulic lines are severed or one of the cylinders malfunctions.